Pertanika 12(1), 47-51 (1989)

COMMUNICATION II

The Rate of Litter Production in Mangrove Forest at Siar Beach,Lundu, Sarawak

ABSTRAK

Penyelidilwn kadar pengeluamn sesarnpah hutan bakau telah dilakukan di Pantai Siar, Lundu, Samwak.Hutan ini mempunyai sembilan spesies pohon; spesies pohon yang dominan ialah Rhizophom mucronata,sementam R, ajJiculata sebagai spesies kodorninan. Kadar pengeluamn sesarnpah ialah 5.72 t/ha/tahun,dan dmijumlah ini 4.49 t/ha/tahun (78.5%) adalah serasah daun. Comk kadarpengeluamn sesarnpahdan serasah daun berubah antam satu bulan dengan lainnya. Pengeluamn sesampah antam bulan AP1ilhingga .fun dan Disernber hingga Februari lebih banyak berbanding dengan bulan-bulan lain.

ABSTRACT

A study of litter production was conducted at Siar Beach, mangrove forest, near Lundu, Samwak. There arenine sppcies oj trees in this jorest oj which Rhizophom mUCTonata is the dominant and R. apiculata is theco-dominant species. The mte oj litter production was 5.72 t/ha/year, and oj this 4.49 t/ha/year (78.5 %)was leaf litter. The production oj litterJluctuates being higher during April to June and December to Februarycompared to other months.

INTRODUCTION

Mangrove trees serve many functions. Theecological functions of mangrove as a landbuilder and coastline stabilizer have beendescribed by McNae (1974) and de la Cruz(1979). Heald and Odum (1970) describedmangrove as a spawning and nursery area forfishes and prawn. These functions, are closelyrelated to the primary productivity of themangrove. Several authors have conductedstudies on the relationship of primary produc­tivity of mangroves and its ecological and eco­nomic functions (e.g. Golley et al. 1962; Healdand Odum 1970; Odum 1971). They foundthat most of the organic debris that enrichedthe estuary were derived from adjacent mang­rove forest. Thus, litter production plays an im­portant role in maintaining the fertility of themangrove ecosystem and supply of food mate­rial to the faunal life (SIivastava 1980). How­ever, the rate of litter production varies fromplace to place, and between species dominatingthe site (Mathias 1974). Such differences canbe seen from the work of Heald (1971) inFlorida, Christensen (1978) in Thailand and

Gong et al. (1984) in Matang mangrove forest,West Malaysia.

The production of litter of the mangroveforest at Siar Beach, near Lundu was studied inorder to understand more about the producti­vity of mangrove ecosystems in Sarawak.

Study AreaThe study area is located at Siar River Estuary,between latitudes 109° 52' E to 109° 53' E andlongitudes 1° 44' to 1° 45' N (Wolfenden andHaile 1963). The estuary is about 12 km N - Eof Lundu (Fig. 1). The river is about 2 m wideat low tide and 4 m wide at high tide.

The area is dominated by Rhizophomrnucronata and R. apiculata is co-dominant(Saberi 1984). The other species that can befound in the area are Bruguiera gyrnnorrhiza, B.paroiflom, B. cylindrica, Avicennia alba, Lurnnitzemsp., Nypa jruticans, Oncosperma sp. and a fernAcrosticum sp.

The soils of the area derived from biotiteadamellite rocks. The climate is reasonably wet,highest precipitation occurring in January, andlowest in March. The total precipitation is 4260mm per year. The temperature varies between

48

N

fSIAR RIVER

SABERI OTHMAN

109 0 51' . E

SOUTH CHINA SEA

SOUTH CHINA SEA

o 1.6 KmI I

Fig. 1. Sial' beach oj Lundu, Sarawak.

PERTANIKA VOL. 12 NO. I, 1989

1 04 1 I

THE RATE OF L1TIER PRODUCTION IN MANGROVE FOREST AT SIAR BEACH, LUNDU, SARAWAK

25° - 28°C, the lowest being in January andhigher in May (Fig. 2).

1000

The total small litter and leaf litter pro­duction varies between forest and climaticregions. Generally leaf litter accounts for morethan 50% of the total litter produced. However,the amounts of this litter may vary dependingon the size of the traps used. For some forests,particularly mangrove, leaf litter could reach ashigh as 80%. A similar high percentage (78.5%)ofleaflitter was detected in the mangrove forestat Siar Beach (Fig. 3).

50

MATERIALS AND METHODS

Plant litter was collected in a trap made of sail­cloth, with a square wooden-frame openingmeasuring 50 x 50 cm. The trap was placed 1mabove the ground. Fifteen such litter traps weresited randomly beneath the trees, and theircontents were emptied at the beginning of eachmonth. The litter was sorted into leaves and amiscellaneous component. The litter was washedand oven-dried at lO5°C to constant weight.

20

Fig. 2. The climatic diagram Jm" Kitching, Sarawak.

MJA SONDJ

o r.eaf-li tter

t?Za r;:is-::ellaneoua

1983 1984

M A M

10

Fig. 3. The pattern oj litterJail J01" 1983 and 1984 in a standoj Mangrove Jorest, Sial' Beach, Lundu, Sarawak.

40

\~

~ 30

.§20

10

)0

,'I'll1"/\1

.' ,

RESULTS AND DISCUSSION

The suitable size and form of litter-trap forsampling litter-fall in a tropical rain forest is notknown. A study of previous work shows that avaried size of litter-traps were used. The small­est was 45 x 45 cm (Woodroffe 1982) and thelargest was 200 x 200 cm (Duke et al. 1981).The form of the trap also shows variation. Mason(1970) had used round shaped traps instead ofsquare, and Kira et al. (1967) used a long beltof plastic net as the trap. In this study a trapwith a square opening measuring 50 x 50 cmwas used. This size is within the range of thetrap used by previous workers, and easy tohandle while in the forest.

The mean values obtained for the mixedmangrove forest at Siar Beach are 5.74 and 4.49t/ha/year for total small litter and leaf litterrespectively. These values are significantly lowerthan those obtained for many tropical rain forest(e.g. Nye 1961; Bullock 1973; Gong et al. 1984).The leaf litter of this forest is about 40% lowercompared to the values obtained for othermangrove forests. This could be due to the factthat the mangrove forest at Siar Beach is not asdense compared to other forests. Such situationshave been highlighted by Gong et al (1984)for Matang mangrove forest, and Woodroffe(1982) for Tuff Crater, mangrove forest, Auck­land New Zealand. The density of trees at SiarBeach is 166/ha (Saberi, 1984), and this value

PERTANlKA VOL. 12 NO. 1,1989 49

SABERI OTHMAN

is about four times lower compared to other fo­rests such as at Banyu Asin, Sumatera (Soekardjoand Kartawinata 1979), Sabah, Malaysia (Liew1977) and in Florida, U.SA (Pool et al. 1977).However, there is no data available for compa­rison on the relationship between density andlitter production in mangrove forests.

Litter production increased in March andApril and reached its highest rate in May. Itsubsequently dropped inJune,July and Augustand remained constant till November. It thenincreased again in December and reached itssecond peak in February. A similar pattern inlitter fall has been reported for Pasoh (Lim1978), Matang mangrove forest (Gong et al.1984) and R. apiculata in Phuket, Thailand(Christensen and Wium-Anderson, 1977). Thehigh production in May coincide with hightemperature and draught. Gill and Tomlinson(1969 & 1971) in their studies of the red mang­rove in South Florida, report peak rates of leaffall and growth during summer months whenair temperature and incident light were at theirannual peaks. Similar results have been reportedby Heald (1971). Snedaker and Lugo (1973)found indications that leaf fall increases duringdry periods. According to Lugo and Snedaker(1975) the timing of these events has a signifi­cant interaction with the hydrologic budget andprimary productivity of the forest community.The higher production in February cannot beexplained in terms of biological processes.However, its does coincide with heavy winds ofthe South China Monsson and rainfall. Occa­s~onal storms have been reported to coincidewith increased litter fall (e.g. Pool et al. 1975;Goulter and Allaway 1979).

Production of litter is relatively continu­ous, thus supplying the detritus food chain. Thefraction exported to adjacent sea areas is notknown, but many leaves are carried away bytides, especially at spring tide's, before anydegradation takes place.

SABERI OTHMAN

Department of Biology,Faculty of Science and Environmental StudiesUniversiti Pertanian Malaysia43400 UPM Serdang, Selangor Darul Ehsan,

Malaysia.

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THE RATE OF LInER PRODUCTION IN MANGROVE FOREST AT SIAR BEACH, LUNDU, SARAWAK

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(Received I I March, I 987)

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